Anti-offset powder comprising dextrose powder and silicone resin treated starch and method of preventing offset from freshly printed papers



United States Patent ANTI-OFFSET POWDER COMPRISING DEXTROSE POWDER ANDSILICONE RESIN TREATED STARCH AND METHOD OF PREVENTING OFF- SET FROMFRESHLY PRINTED PAPERS James E. Fenn, Paterson, N.J., assignor toOxy-Dry International Inc., New York, N.Y., a corporation of New York NoDrawing. Filed Dec. 28, 1967, Ser. No. 694,062

Int. Cl. C08b 25/02; B41f 23/06 US. Cl. 260-9 4 Claims ABSTRACT OF THEDISCLOSURE An effective, improved anti-offset powder particularly usefulin offset planography and especially useful in antioffset devices inwhich the powder is electrically charged prior to being dispensed fordeposition on the freshly printed impression is provided with acomposition comprising :a mixture of dextrose having an average particlesize of about 100;]. and containing from 10 to 25% of a hydrophobicpowder, such as a starch treated with a silicone resin to render thestarch or other particles hydrophobic. A thin film of this powdereffectively prevents olfsetting from one sheet to another in thedelivery stack, while allowing long press runs without contaminating theink rollers or clogging of the printing plates.

SUMMARY The invention provides an anti-offset powder which is especiallyadapted for use in printing by offset planography and is to be depositedas an exceedingly thin coating on the freshly printed sheets just priorto their being deposited on the delivery stack, thereby preventing thefreshly printed impression on one sheet from being offset onto the backof the succeeding sheet deposited in the same stack.

The powder of the present invention comprises from 75 to 90% by weightof finely divided dextrose having an average particle size of from 50 to150 preferably about 100 with which is thoroughly mixed from 10 to 25%of a hydrophobic silicone resin treated starch, and if desired from 0.5to 0.03% of a free-flowing agent such as finely dividedsodium-silico-aluminate or tribasic calcium phosphate.

The powder is preferably applied to the printed sheet by anelectrostatic sprayer such as an Oxy-Dry sprayer typically illustratedin US. Patent No. 3,292,046.

OBJECT The present invention has for its object the provision of a noveland improved anti-offset powder especially adapted for use withelectrostatic sprayers of the Oxy- Dry type as disclosed in US. PatentNo. 3,292,046, and more especially in connection with offsetplanography; and to a process using such powder.

As used herein, anti-offset refers to the prevention of offset orsmutting from the freshly printed face of one sheet to the back face ofa subsequent sheet as they are laid down in a delivery pile. Offsetplanography refers to the printing process in which a planographic plateis moistened and inked and the ink is then transferred to a resilientblanket atfer which an ink impression is transferred to a sheet or webof paper or other material.

PRIOR ART In the prior art many powder comprising corn, tapioca,arrowroot or potato starch have been used to prevent offset inletterpress printing and offset planography. Sometimes these starchpowders have been combined with a 3,491,036 Patented Jan. 20, 1970 smallcontent of tribasic calcium phosphate to improve their flowcharacteristics.

Additionally, anti-offset powders consisting essentially of starchparticles coated with a small amount of a thermoset polysiloxane resinhave been used, as disclosed in U.S. Patent No. 2,647,892. I

More recently, according to British Patent No. 834,700 it has beenproposed to use refined sucrose of a grain size from 20, to 40011. as ananti-offset powder, to which may be added a minor amount (about 2%) oftri-basic calcium phosphate.

All of the foregoing have their several disadvantages in use. Ananti-offset powder comprised essentially of starch tends to clog theblanket, ink-rollers and printing plates and interferes with the layingdown of a subsequent impression on top of a first impression treatedwith such an anti-offset powder, thereby producing a splotchy print.Additionally the excess powder deposited on the printed and unprintedareas imparts a rough, undesirable feel to the surface and causes feedback of the starch to the inkrollers and printing plates requiringfrequent shut-downs and time consuming cleaning of the ink-rollers andprinting plates.

Hydrophobic, resin-coated starch particles, by themselves, are alsosubject to disadvantages. The relatively large quantity of suchhydrophobic starch particles needed to prevent offset from one printedsheet to the other face of another sheet, provides an excessively largequantity of starch on the imprinted areas, and while it improves, itdoes not eliminate the clogging of the ink-rollers, the filling of theprinting plates, nor the blotching of a subsequent impression Where theink is printed onto a starch coated white portion of the sheet.

Powdered sucrose, with or without a small amount of tribasic calciumphosphate is disadvantageous for use in anti-offset sprayers due to thehygroscopic character of the sucrose. It cannot ordinarily be usedexcept in atmospheres of low humidity such as much less than 50% RH.Except in extremely dry atmospheres, powdered sucrose lumps, does notfeed uniformly and consequently results in an uneven and ineffectivedeposit of anti-offset powder on the impressions. If too little powderis deposited, offset occurs, the sheets tend to stick together; if toomuch powder is deposited, a subsequent impression, as in two color ormulti-color printing, tends to be splotchy, and the sheet surface isleft with an uneven, rought surface which represents an undesirablefeeling to the reader.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the presentinvention, the improved antioifset powder consists essentially of a wellmixed mixture of Percent by weight Dextrose powder -90 Silicon resintreated starch 10-25 Free flowing agent 0.5-0.03

preferably:

Dextrose powder Silicon resin treated starch 15 Tribasic calciumphosphate, finely ground 0.2

The dextrose is preferably a substantially pure food grade of commercialdextrose having an average particle size of about 50 to 150 preferablyand is free flowing, hydrophilic but not hygroscopic, as is sucrose. Thestarch powder may be made from any of the starches and have an averageeffective size as shown below:

Corn starch About 1511.. Tapioca starch About 2011.. Arrowroot starchAbout 40-45 Potato starch About 70-75,u..

What ever starch powder is used, it is treated to render it hydrophobicand one such treatment is disclosed in the prior U.S. patent to La Brieand Penn, No. 2,647,892 where the starch is treated with a low viscositythermosetting silicone resin, which is distributed uniformly over theindividual starch particles and is then treated as disclosed in US.Patent No. 2,647,892, to render the starch particles hydrophobic.

Where a free flowing agent is included in the hydrophobic resin-treatedstarch it may comprise finely ground sodium-silico-aluminate or tribasiccalcium phosphate in an amount from 5.0 to 2.5% of the starch componentor up to about 0.2% of the total powder to be sprayed. The preferredsilicone resin for treating the starch is the same as disclosed in US.Patent No. 2,647,892, and may be applied in the same manner as describedin said patent.

The dextrose powder and hydrophobic starch, and free flowing agent ifused, are thoroughly blended and are then ready for use. Due to thenon-hygroscopic properties of the dextrose and resin-treated particles,the powder may be stored for long periods of time at relatively highhumidity without impairing its usefulness.

Also in use, the combined dextrose and hydrophobic starch mixtureprovides many additional and unexpected benefits.

As distinct from sucrose, the dextrose powder maintains its particulategranularity without the lumping which occurs with powdered sucrose evenin atmospheres of moderate R.H.

As compared with the powder of US. Patent No. 2,647,892, the presentinvention allows the use of only a very minor amount of the hydrophobicstarch powder so that the press run can be extended to a great extentbefore cleaning, and at no time is a sufficient quantity of thehydrophobic starch deposited on the printed sheet to impair a subsequentover-printed impression, nor to create an undesirable tactile sensationas the surface of the printed sheet is felt by the fingers of a reader,the resin-treated starch is gradually absorbed into the ink impression,and is present in only a minor amount so that its presence on theimprinted areas of a sheet creates no problem.

The dextrose powder, being only hydrophilic and not hygroscopic does notlump under humid operating conditions and is always available foruniform delivery by an electrostatic sprayer.

As the finely divided dextrose with its minor addition of hydrophobicstarch is deposited on the freshly printed surface of a sheet thedextrose and hydrophobic starch on the ink impression are adhered to theoleagenous layer on the sheet but retain their shape so as to providethe proper mechanical spacing of the freshly printed surface from theback of the next sheet laid down in the delivery pile.

The dextrose powder particles which are deposited on those parts of thesheet which do not have an ink impression printed by offset planographyare gradually absorbed by the moisture on the face of the sheet, thismoisture having been transferred from the moistened non-printing areasof the planographic printing member. The hydrophobic starch particlesare not absorbed, but are present in such a minor amount that they donot interfere with the laying down of a subsequent impres- 4 sion of adifferent color in the previously imprinte areas, and some of thehydrophobic starch particles will be lost in the handling of the sheetbetween the first and second impression or between one impression and alater third or fourth impression.

The dextrose absorbed into the slightly moist surface of the paper doesnot impair the color nor does it provide an ink-rejecting surface toimpair the quality of a subsequent impression.

The free flowing agent is present in such minute amounts that it doesnot interfere with obtaining the finest quality of subsequentimpressions.

In use, the anti-offset powder of the present invention is applied tothe surface of a sheet or web freshly printed by offset set planography,after which the web is rewound into a roll, or the successive sheets arestacked, one on top of another in the delivery of the press. The rate atwhich the powder is applied will vary widely depending upon the type ofpaper and the amount of ink being used, but ordinarily from 2 to 5ounces of anti-offset powder per 1,000 square feet of paper printed,usually about 3 ounces per 1,000 square feet.

Although the invention finds its greatest usefulness in offsetplanography, the powder may be similarly used in letter-press printing,although in that case the dextrose will not normally be absorbed intothe dry unprinted areas of the sheet.

What is claimed is:

1. An anti-offset powder comprising from to by weight dextrose powder,and from 10 to 25% by weight of hydrophobic, silicone resin treatedstarch having a particle size of from 15 to 75 the average particlesizes of the dextrose particles being from 50 to 150g.

2. An anti-offset powder according to claim 1 in which the averageeffective dextrose particle size is about p and the powder consists ofPercent by weight Dextrose 84.98

Hydrophobic, silicone resin treated starch 15.0 Free flowing agentcomprising sodium-silico-alumi nate or tribasic calcium phosphate 0.2

3. The method of preventing offset from a freshly printed surface of asheet to an adjacent sheet in a delivery in offset planographic printingwhich comprises applying to the freshly printed face of a sheet ananti-offset powder cOmprising finely divided particles of dextrose 75 to90% by weight, hydrophobic, silicone resin treated starch 10 to 25% byweight, the average particle size of the dextrose being from 50 to andthe average effective size of the starch particles being from 15 to 754. The method of claim 3 in which the powder consists of dextrose 84.98%by weight, hydrophobic, siliconeresin treated starch 15.0% by weight andfrom 0.5 to 0.03% by weight of a free flowing agent comprisingsodiumTsilico-aluminate or tribasic calcium phosphate, the dextroseparticles having an average size of about 100 and the starch having anaverage effective size of from 15 to 75,u.

References Cited UNITED STATES PATENTS 2,322,736 6 /1943 Pike 106-1242,647,892 8/ 1953 La Brie 2609 2,673,520 3/1954- Bainbridge 101-422WILLIAM H. SHORT, Primary Examiner E. WOOD'BERRY, Assistant Examiner US.Cl. X.R. 101-422

